Although astronauts last walked on the Moon in 1972, the exploration of the Moon with robotic spacecraft has sporadically continued through the years since, with some exciting developments in recent years - including verification of water on the Moon.

Lunar Reconnaissance Orbiter (LRO)

Among the more recent probes sent to the Moon is the Lunar Reconnaissance Orbiter (LRO), launched by the United States in 2009. The NASA Goddard Spaceflight center robotic spacecraft orbiting the Moon on a polar mapping orbit, is a precursor to future manned missions to the Moon. When launched, it was the first U.S. lunar mission in more than 10 years. LRO's detailed mapping program is identifying safe landing sites, locating potential resources, characterizing the radiation environment and demonstrating new technology.

Payload

The LRO payload, comprising six instruments and one technology demonstration, is providing key data sets to enable a human return to the Moon. The instruments include:

Lunar Reconnaissance Orbiter Camera (LROC) retrieves high-resolution black and white images of the lunar surface, capturing images with resolutions down to 1m and imaging the lunar surface in color and ultraviolet to enable safe landing site selection.

ResultsEven with some initial failures, LRO has already collected as much data as all other planetary missions combined. It has identified, among other things, hardware still remaining at the six Apollo landing sites.

Here are some key results:

The first images from LRO were published on July 2, 2009, showing a region in the lunar highlands south of Mare Nubium (Sea of Clouds)

On Aug. 21, 2009, the spacecraft, along with the Chandrayaan-1 orbiter, attempted to perform a bistatic radar experiment to detect the presence of water ice on the lunar surface; the attempt was a failure because Chandrayaan-1 radar was not pointed at the Moon during the experiment.

On Dec. 17, 2010, the most accurate topographic map of the Moon to date based on data gathered by the LOLA instrument was released to the public.

On March 15, 2011, the final set of data from the exploration phase of the mission was released to the NASA Planetary Data System; among the latest products is a global map with a resolution of 100 meters per pixel from the LROC.

Lunar Crater Observation and Sensing Satellite (LCROSS)

The LRO also carried with it the Lunar Crater Observation and Sensing Satellite (LCROSS). Managed and operated by NASA Ames Research Center working in conjunction with spacecraft and integration partner Northrop Grumman and launch partner United Launch Alliance,

LCROSS sought to confirm the presence of water ice in a permanently shadowed crater near a lunar polar region. Concentrated hydrogen signatures had been detected in that area in 1999 by NASA's Lunar Prospector.

The mission employed the unusual technique of crashing a spacecraft into the Moon in order to observe and analyze the resulting debris plume created by the impact.

Holding on to a Centaur upper stage booster rocket, the LCROSS shepherding spacecraft orbited the Earth and Moon for several months to achieve the mission's optimal impact angle, which was important to accomplish the largest debris plume possible. Plus, the long orbit depleted the spacecraft's fuel supply to prevent lunar contamination. On Oct. 9, 2009, the Centaur rocket separated from the LCROSS sheparding spacecraft and crashed into the Cabeus crater near the south pole of the Moon. Following four minutes behind the Centaur, the LCROSS shepherding spacecraft passed through the resulting debris plume, collecting and relaying data until it also crashed into the crater.

Using spectrometers, cameras and a radiometer, LCROSS captured data of the debris plume as it encountered sunlight, which causes water-ice, hydrocarbons or organics to vaporize and break down into their basic components. In November 2009, NASA scientists confirmed that the plume did, indeed, contain water ice - in larger amounts than originally suspected. This is an important finding that could influence future lunar exploration.

Gravity Recovery and Interior Laboratory (GRAIL)

During 2011, NASA launched its Gravity Recovery and Interior Laboratory (GRAIL) mission to circle the Moon with a pair of small spacecraft called Ebb and Flow, which were designed to precisely map the lunar gravity field. As the spacecraft fly over areas of greater and lesser gravity, caused both by visible features such as mountains and craters and by masses hidden beneath the lunar surface, they move slightly toward and away from each other. An instrument aboard each spacecraft precisely measures these changes – calculating variations as slight as one-tenth of one micron or about half of a human hair. Scientists are translating this information into a high-resolution map of the Moon's gravitational field.

The two GRAIL spacecraft are near-twins, each about the size of a washing machine, with minor differences resulting from the need for Flow to follow Ebb as they circle the Moon.

ach spacecraft carries a set of cameras for MoonKAM (Moon Knowledge Acquired by Middle school students), marking the first time a NASA planetary mission has carried instruments expressly for education and public outreach.

MoonKAM is led by Sally Ride Science in collaboration with undergraduate students at the University of California in San Diego. More 2,700 schools in 52 countries have signed up to participate in MoonKAM.

In a NASA competition, Ebb and Flow were named by fourth grade students at Emily Dickinson Elementary School in Bozeman, Mont. (pictured, right).